1. Field of the Invention
This invention relates to a network system and a network connection device, and in particular to a network system and a network connection device in which default routes are set up.
2. Description of the Related Art
In a general routing technique, the routing mechanism taken for a network connection device, such as a router, is that, if a next hop does not exist in a routing table of the network connection device, data packets are transmitted according to a default route. The default route is a predetermined destination for the network connection device and it is expressed by “0.0.0.0 to next hop” for example.
Japanese Laid-Open Patent Application No. 2002-359638 discloses a method of controlling a router system to ensure that a default route is always set in a routing table.
However, a default route is the only one piece of routing information that can be set up in a certain network. Namely, it has been handled so that one default route in a network is recognized in common. Therefore, it has been impractical that a plurality of default routes be set up for every network connection device or every segment of a certain base.
To solve the problem that a plurality of default routes cannot be set up, a method of the policy routing is used in a conventional network connection device. The policy routing is the routing mechanism in which both a transmission source address and a destination address are checked to specify a destination route and data packets are transmitted to the target destination.
However, the method of policy routing has the following problems. The first problem of policy routing is that the number of routes that can be set up depends on the performance of a network connection device and it is limited. The second problem of policy routing is that the manner of setting routes is complicated and difficult. For example, in a case of Internet connection, describing all the global addresses which exist in the world will be needed for the method of policy routing and a large amount of setting information will be needed. This makes the management of the configuration information complicated.
The third problem of policy routing is that, when the necessity of setting addition or deletion occurs, the setting modification work for all the network connection devices has to be carried out.